Because of their geochemical properties, rare earth elements (REEs) are typically dispersed and not often found concentrated as rare earth minerals in economically exploitable ore deposits. It was the very scarcity of these minerals that led to the term “rare earth.” Some of the major end uses for rare earth elements (REEs) include catalysis, permanent magnets and rechargeable batteries for hybrid and electric vehicles, phosphors in lighting and flat panel displays (e.g., cell phones, portable DVD players, laptops), generators for wind turbines, numerous medical devices, and many other applications in the fast growing green energy and high tech market segments. In 2010, the U.S. Department of Energy classified several REEs critical to these markets to be in short supply, including yttrium (Y) and lanthanides including terbium (Tb), neodymium (Nd), europium (Eu), and dysprosium (Dy). China, the world's largest REE supplier, controlling about 95% of the market, has declared that China's heavy REEs (including Y and lanthanides Eu, Tb, and Dy) could be depleted in the next 15-20 years.
Lanthanides are usually obtained mixed together from ore concentrate and are problematic to separate due to their well-pronounced chemical similarity. Classical separation techniques are time consuming, require elaborate multistage processing sequences, and use expensive (and generally hazardous) reagents which can contaminate the product and the environment. Industrially, the REEs usually are recovered from the leach liquor by solvent extraction with 25% di-(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene, followed by multistage pulling of the rare earths from the organic solution and precipitation with oxalic acid. The final step is calcination and transformation of the rare earth oxalates into oxides. Less than 1% of the REEs are recycled from end-of-life products mainly due to the complexity of these methods involving large-scale use of hazardous chemicals (e.g., organophosphorous reagents) and inefficient recycling routes.